IC‐P‐048: Estimating and Accounting for The Effect of MRI Scanner Hardware Changes on Longitudinal Whole‐Brain Atrophy Measurements
Bibliographic record
Abstract
Longitudinal MRI studies are often subjected to scanner hardware changes or upgrades, which may alter image characteristics such as contrast, signal-to-noise ratio, intensity non-uniformity and geometric distortion. This renders measurements of brain atrophy potentially unreliable as it may introduce non-physiological brain volume fluctuation across the point of hardware change. Mixed-effects modelling is one way to estimate rates of brain atrophy while identifying and correcting this bias. We analyzed 680 control, mild cognitive impairment (MCI), and Alzheimer’s disease (AD) subjects who were scanned at 1.5T for the Alzheimer’s Disease Neuroimaging Initiative (ADNI) phases 1, GO, and 2. The subjects were initially scanned on 10 different scanner hardware models from GE, Siemens, and Philips. 442 subjects continued with the consistent scanner model throughout the follow-up up to 8 years, but 238 subjects were subject to intra- or inter-vendor MRI scanner hardware upgrades or changes during the study. A total of 3411 T1-weighted scans were pre-processed using a cross-sectional pipeline including nonparametric non-uniform intensity normalization.[1] Then, the percentage brain volume changes (PBVCs) between the follow-up scans and the baseline “screening” scans were calculated using FSL-SIENA.[2] A mixed-effects model with subject-specific random slopes and intercepts was applied to estimate the fixed effect of scanner hardware changes on the PBVC measures. The same model also included a term to estimate the fixed effect of a scanning sequence change from MP-RAGE to IR-SPGR in some subjects. Significant fluctuations in PBVC were found across the following hardware upgrade or change combinations (SE; p): Siemens Symphony to SymphonyTIM -0.5% (0.1; p<0.0001); Philips Intera to Siemens Avanto -1.6% (0.5; p=0.001); GE Excite to GE HDx 0.2% (0.07; p=0.002); GE Excite to GE HDxt 0.3% (0.1; p=0.02). The change of sequence from MP-RAGE to IR-SPGR was associated with an average -1.5% (0.1; p<0.0001) change. Different scanner combinations also showed different biases. Scanner hardware and pulse sequence changes have significant effects on estimation of brain atrophy rates. If suitable data are available, it may be possible to explicitly account for these during the analysis.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".